HLA Class I expression on tumor cells is involved in the anti-tumor immune response. Using known melanoma cell lines, we assessed expression of the A and B loci on cell membranes using monoclonal antibodies before and after treating the cells with interferon. We concluded that the A locus is expressed in melanoma cultured cell lines and is not up-regulated with interferon gamma. The B locus is frequently down regulated but is sensitive to interferon gamma upregulation. We are now using these same techniques on melanoma patients by performing fine needle aspirations of superficial melanoma lesions before and after treatment with interferon gamma or interleukin 2.